Effective exposure dose monitoring technique in extreme ultraviolet lithography

Extreme ultraviolet (EUV) lithography is a promising candidate for 2x-nm-node device manufacturing. Management of effective dose is important to meet the stringent requirements for critical dimension control. As a test pattern for a lithography tool evaluation, the effective dose monitor (EDM) demonstrates sound performance in dose monitoring for optical lithography, such as KrF lithography. The EDM can measure an exposure dose with no influence on defocus, because the image of an EDM pattern is produced by the zeroth-order ray in diffraction only. When this technique is applied to EUV lithography, the mask shadowing effect should be taken into consideration. We calculated the shadowing effect as a function of field position and applied it to correction of the experimental dose variation. We estimated the dose variation in EUV exposure field to be 2.55% when corrected by the shadowing effect. We showed that the EDM is useful for EUV lithography.